It has been heretofore known to apply coating liquid containing organic dyes having lyotropic liquid crystallinity, on a substrate, and then to dry the coating liquid to form a polarizing layer on the substrate.
The surface of a substrate is typically provided with an alignment regulating force by an alignment treatment (e.g., a rubbing treatment). Thus, the organic dyes contained in the coating liquid are aligned in a predetermined direction due to the alignment regulating force on the surface of the substrate. Then, drying the applied coating liquid causes the alignment of the organic dyes to be fixed, and thus a dry coating film (polarizing layer) having light polarization properties is formed on the substrate.
However, depending on the formation material of the substrate, the organic dyes cannot be aligned, or is difficult to align, in a predetermined direction by merely providing an alignment treatment on the surface of the substrate.
To solve this problem, it is known to form an alignment layer containing a polyimide based resin (hereinafter referred to as “polyimide based alignment layer”) on a substrate, to apply application liquid containing organic dyes on this polyimide based alignment layer, and then to dry the application liquid to form a polarizing layer (see, e.g., Patent Document 1). A polyimide based alignment layer contains a polyimide based resin therein, and has a surface on which an alignment treatment has been performed.
However, a polyimide based alignment layer does not have a sufficient level of an alignment regulating force. This poses a problem in that, depending on the organic dye material, the organic dye may not be sufficiently aligned on the alignment layer, which may degrade the light polarization properties of the polarizing layer.
Moreover, formation of a polyimide based alignment layer requires application, on a substrate, of application liquid containing polyamic acid, which is a precursor of polyimide, and firing of this coating film at a high temperature (around about 200° C.) to imidize the polyamic acid. If the firing temperature of the coating film is higher than the glass transition temperature (Tg) of the substrate, the substrate will be heated to a temperature above its glass transition temperature during firing. Heating the substrate to a temperature above its glass transition temperature may result in a change in characteristics, such as the mechanical strength and/or optical characteristics, of the substrate. Thus, formation of a polyimide based alignment layer requires use of a material having a glass transition temperature higher than such firing temperature, as the formation material of the substrate. In other words, a problem exists in that formation of a polyimide based alignment layer on a substrate places a restriction on the formation material of the substrate. In particular, when the formation material of the substrate is a resin, the glass transition temperature of the resin is typically often lower than the firing temperature, and thus, it is not feasible to form an alignment layer on various types of resin substrates.    [Patent Document 1] JP 2006-47966 A